无线局域网中的TCP性能增强技术研究

发布时间：2019-06-04 21:03

【摘要】：近几年来,无线网络得到了快速的发展,尤其是基于IEEE 802.11协议族的基础结构型无线局域网。由于具有易于部署、成本低和支持移动性等特点,该类无线局域网被广泛应用于世界各地。此外,越来越多的移动设备都支持与无线局域网的连接,进一步推动了无线局域网的发展。统计数据表明,基础结构型无线局域网中传输的主要业务是基于TCP协议的。然而,传统的基础结构型无线局域网并不能很好的为TCP业务提供服务。无线局域网中无线信道的特性和用户的移动性对TCP拥塞控制机制产生了负面的影响,使得无线局域网传输TCP业务时吞吐量较低。除此之外,无线局域网使用的DCF机制限制了AP接入无线信道的能力,导致无线局域网中的上、下行TCP数据流的吞吐量具有较大差距。基础结构型无线局域网中的这种上、下行TCP数据流不公平的现象,在机场和大型会议等场所,表现得尤为明显,严重影响了用户的体验。在这种情况下,为了有效地提升无线局域网的服务质量,我们有必要对无线局域网及TCP拥塞控制机制之间的问题进行研究。在本文中,我们根据国内外相关研究的现状,采用理论分析与实验评估相结合的技术路线,研究了无线局域网中的TCP性能增强技术。本文中的主要工作概括如下:1.概述了无线局域网的网络结构、标准化进程及其使用的接入协议的主要内容。同时,分析了TCP协议拥塞控制机制的基本原理及其应用于无线局域网时遇到的一些问题。2.详细地介绍了目前无线局域网中主要的TCP性能增强技术,同时对其中典型技术的优缺点进行了分析。3.结合无线局域网及TCP协议拥塞控制机制的特点,提出了一种自适应流控代理的方法。该方法不需要修改无线局域网的底层协议,易于实施。自适应流控代理实施于AP的IP层,可以提供TCP代理的功能,以减小无线局域网中无线信道及用户移动性对TCP业务的负面影响。此外,该方法能够监控经过AP的流量信息,并根据统计的流量信息,周期性地计算出无线局域网的传输能力和其中每个TCP数据流对应的往返传输时延。该方法利用计算出的结果,进一步求出每个TCP数据流应使用的滑动窗口值,并利用计算出的值,修改对应TCP ACK报文的窗口域,以控制每个TCP数据流的吞吐量。通过这种方式,自适应流控代理可以在充分利用无线局域网传输能力的同时,尽量减小无线局网中上、下行TCP数据流吞吐量的差距,以提升用户的体验。4.利用NS-3对通信场景进行仿真,验证了自适应流控代理的有效性。利用仿真场景,我们做了三组仿真实验。我们在第一组仿真实验中不对无线局域网中的AP进行任何修改;在第二组仿真实验中修改AP的MAC层,以实现自适应优先级控制功能;在第三组仿真实验中修改AP的IP层,以实现自适应流控代理功能。在每一组实验对应的子实验中,我们改变了WLAN中站点的数量以及WLAN传输的业务类型,以研究每个方法在不同条件下性能的变化趋势。为了得到较为准确的统计结果,我们利用不同的随机数种子,对每一组子实验进行多次重复的试验。我们利用WLAN的总吞吐量、下行TCP数据流的平均吞吐量和不同TCP数据流之间的公平性来衡量WLAN的性能。通过仿真结果,容易看出自适应流控代理可以有效地提升WLAN的性能。
[Abstract]:In recent years, the wireless network has been developed rapidly, especially based on the basic structure type wireless local area network based on the IEEE 802.11 protocol family. The wireless local area network is widely used in various parts of the world due to the characteristics of easy deployment, low cost, and support mobility. In addition, more and more mobile devices support the connection with the wireless local area network, and further promote the development of the wireless local area network. The statistics show that the main traffic in the base-structured wireless local area network is based on the TCP protocol. However, the traditional infrastructure type wireless local area network can not provide service to the TCP service well. The characteristics of the wireless channel and the mobility of the user in the wireless local area network have a negative influence on the TCP congestion control mechanism, so that the throughput is low when the wireless local area network transmits the TCP service. In addition, the DCF mechanism used by the wireless local area network limits the ability of the AP to access the wireless channel, resulting in a large gap in the throughput of the up and down TCP data streams in the wireless local area network. In the base-structured wireless local area network, the phenomenon of the unfairness of the downlink TCP data is especially obvious in the fields such as the airport and the large-scale conference, and the experience of the user is seriously affected. In this case, in order to effectively improve the service quality of the wireless local area network, it is necessary to study the problem between the wireless local area network and the TCP congestion control mechanism. In this paper, we study the technology of TCP performance enhancement in wireless local area network based on the current situation of domestic and foreign research and the combination of theoretical analysis and experimental evaluation. The main work in this paper is as follows:1. The network structure, the standardization process and the main content of the access protocol used in the wireless local area network are summarized. At the same time, the basic principle of the congestion control mechanism of the TCP protocol and some problems encountered in the application of the wireless local area network are analyzed. In this paper, the main TCP performance enhancement technology in the wireless local area network is introduced in detail, and the advantages and disadvantages of the typical technology are analyzed. Based on the characteristics of the congestion control mechanism of the wireless local area network and the TCP protocol, a self-adaptive flow control agent is proposed. The method does not need to modify the bottom layer protocol of the wireless local area network and is easy to implement. The adaptive flow control agent is implemented in the IP layer of the AP, and the function of the TCP proxy can be provided to reduce the negative influence of the wireless channel and the user mobility on the TCP service in the wireless local area network. In addition, the method can monitor the flow information through the AP and periodically calculate the transmission capacity of the wireless local area network and the round-trip transmission time delay corresponding to each TCP data stream according to the statistics flow information. The method further obtains the sliding window value to be used for each TCP data stream by using the calculated result, and modifies the window domain corresponding to the TCP ACK message by using the calculated value to control the throughput of each TCP data stream. In this way, the adaptive flow control agent can reduce the gap of the throughput of the upper and lower TCP data streams in the wireless local network to improve the user's experience while making full use of the wireless local area network transmission capability. The communication scene is simulated by NS-3, and the effectiveness of the adaptive flow control agent is verified. Using the simulation scene, we made three groups of simulation experiments. In the first group of simulation experiments, the AP in the wireless local area network is not modified; the MAC layer of the AP is modified in the second group of simulation experiments to realize the adaptive priority control function; and the IP layer of the AP is modified in the third group simulation experiment to realize the self-adaptive flow control agent function. In the sub-experiments corresponding to each set of experiments, we changed the number of sites in the WLAN and the traffic type of the WLAN transmission to study the trend of the performance of each method under different conditions. In order to get more accurate statistical results, we used different random number seeds to test every group of sub-experiments. We use the total throughput of the WLAN, the average throughput of the downlink TCP traffic, and the fairness between the different TCP data streams to measure the performance of the WLAN. Through simulation results, it is easy to see that the adaptive flow control agent can effectively improve the performance of WLAN.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN925.93;TN915.04

【相似文献】